Good news for all Left 4 Dead 2 fans, as Valve announced the game's Workshop has been moved out of beta. Everything from campaigns, items, weapons, and more can be downloaded and installed with ease from the Workshop. The collection is a little barren right now, but that is sure to change once modders add the thousands of campaigns, items, and skins already available.
Valve stresses that only the original creator should upload the content, so just hang tight if some of your favorites aren't there yet. You can always ask the creator to post it if they haven't yet, though Valve says to be nice about it if you go that route.
In order to add content to your copy of L4D2, you can browse in-game or through the Steam client. Click the Subscribe button on something you like, say a new skin or weapon, and wait for it to download. The content automatically starts downloading the next time you start the game if you use the client, while in-game is just a matter of patience.
Uploading content requires updating the Authoring Tools and starting up the Workshop Manager to share your mods. Valve increased the file size limit for the Workshop to 200MB, but larger campaigns are broken up into sub-200MB files. If you're uploading one of those larger campaigns, it must be split the vpk so there's content in each part, like so:
Part 1 Sounds and Scripts
Part 2 Map 1
Part 3 Map 2
Part 4 Materials
Part 5 Models
*Include your missions folder in each part along with your addoninfo.txt file
Once this is done add all your items into a collection and mark it as a "items that work together (will show a 'subscribe to all' button)"
It also makes updating certain sections faster and easier, since only certain parts, like a map, need to be redownloaded instead of the entire campaign. So go on and try out the new L4D2 Workshop, and be sure to check out the appropriate Steam Workshop forum to dicuss it with your fellow gamers.